1. Field of the Invention
The present invention relates to a heating apparatus for a vehicle, which is provided with a heat-generating unit using a shearing force, for increasing a temperature of cooling water for cooling a water-cooled engine.
2. Description of Related Art
Conventionally, as a heating apparatus for a vehicle, there has been generally known a hot water type heating apparatus for heating a passenger compartment, in which cooling water for cooling a water-cooled engine is supplied to a heater core disposed in a duct, and air heated while passing through the heater core is blown into the passenger compartment by a blower to heat the passenger compartment.
Further, in a case of the vehicle where the heat amount generated by the engine is small, such as a vehicle having a diesel engine or a lean burn engine, because the heat amount generated by the engine is too small to heat the cooling water sufficiently, a temperature of the cooling water in the cooling water circuit cannot be maintained at a predetermined temperature (for example, 80.degree. C.), there occurs a problem in that a heating capacity for the passenger compartment is insufficient.
To overcome such a problem, as disclosed in JP-A-2-246823, there has been conventionally proposed a heating apparatus for a vehicle in which a heat-generating unit using a shearing force, for heating cooling water to be supplied to a heater core, is disposed in a cooling water circuit.
The heat-generating unit transmits a rotational driving force of the engine to a shaft through a belt transmitting mechanism and the electromagnetic clutch, a heat-generating chamber is formed in a housing, and a cooling water passage is formed at an outer periphery of the heat-generating chamber. Further, a rotor which rotates integrally with the shaft is disposed in the heat-generating chamber, and a shearing force generated by a rotation of the rotor is applied to viscous fluid such as silicon oil sealed in the heat-generating chamber to generate heat. The cooling water is heated by the generated heat.
However, when a water valve for adjusting a radiating amount of the heater core is disposed on the midway of a cooling water pipe for connecting the heat-generating unit and the heater core, if the water valve is closed, the cooling water does not circulate into the cooling water circuit of the heat-generating unit, with the result that there occurs a problem in that the viscous fluid in the heat-generating chamber is heated abnormally.
Especially when high-viscosity silicon oil is used as the viscous fluid, if a temperature of oil itself as a material of the high-viscosity silicon oil is heated abnormally up to 250.degree. C. or more, there is a possibility that a mechanical deterioration or a thermal deterioration due to the shearing force of the rotor generates. Once the mechanical deterioration or a thermal deterioration generates as described above, the viscosity of the viscous fluid lowers. In this way, thereafter, even if the shearing force is applied to the viscous fluid by the rotor, heat-generating efficiency lowers, and there occurs a problem in that sufficient heating capacity cannot be obtained when the heating operation for the passenger compartment is necessary.